What's going on (I think)
It sounds to me like your proxy server is only sending auth info when the info is actually requested. Most browsers (NS 4, IE, Opera) will send auth info to a site once they have a domain request no matter if they get another request or not. It becomes a sort of cookie. Some browsers, like recent Mozilla builds, will only send the auth info when the HTTP server actually requests it., or for any page under the page the browser authenticated for.
Example: if I have a protected page /forums/forms/content/editReply, and that is the first page for which Mozilla sends auth info, Mozilla will never send auth info for any unprotected page above editReply in the directory hierarchy (eg. /forums/render/showContent). The problem manifests as being logged in for replies, but "not logged in" for unprotected pages. The display pages are unprotected so people can browse anonymously.
How zIWETHEY authentication works:
The only protected pages are the user pref pages and the reply pages. When a user logs in, zIWETHEY redirects the login to a page at the top of the /forums hierarchy in order to trick the browser into always sending the auth info.
I think your proxies might be somehow foiling my hack for Mozilla, because that's exactly the same behavior I got in Mozilla before I added the redirect hack.
Regards,
-scott anderson